A risk assessment should be carried out before any work activity begins, whenever workplace conditions change, and at regular intervals to make sure existing controls still work. Beyond that general rule, specific events trigger mandatory or strongly recommended assessments: introducing new equipment, hiring vulnerable workers, responding to an accident, or even noticing that the weather has shifted on a job site.
Before Work Begins
The most fundamental trigger is the start of any new work activity. Before employees begin a task, someone needs to identify what could go wrong and how to prevent it. This applies to routine operations, one-off projects, and everything in between. If your organization employs five or more people, UK law requires the assessment to be written down and kept on record. Smaller teams still need to carry out the assessment, but it doesn’t have to be formally documented.
This initial assessment is your baseline. It covers the hazards workers will encounter, who might be harmed, and what controls are already in place. Every later reassessment builds on this foundation.
When Something Changes in the Workplace
Any meaningful change to how, where, or with what your team works should prompt a fresh look at risks. The Health and Safety Executive specifically flags changes to staff, processes, substances used, or equipment as triggers for review. Even a seemingly small shift, like switching to a new cleaning chemical or rearranging a production line, can introduce hazards that the original assessment didn’t account for.
Common changes that call for reassessment include:
- New equipment or tools: Different machinery brings different pinch points, noise levels, or electrical risks.
- Changes in staffing: New hires may lack experience with existing hazards, and reduced headcount can mean workers take on unfamiliar tasks.
- Relocation or renovation: Moving to a new building or reconfiguring an existing space changes traffic flow, emergency exits, and exposure patterns.
- New substances: Introducing chemicals, solvents, or biological agents requires a specific hazardous-substance assessment covering exposure routes and safe handling.
After an Accident or Near Miss
An injury, illness, or close call is one of the clearest signals that your current risk controls have a gap. When an incident occurs, you need to evaluate the work environment and duties involved to determine whether workplace conditions caused or contributed to what happened. This isn’t just good practice. Regulatory frameworks in both the UK and the US treat post-incident evaluation as a core employer obligation.
Near misses deserve the same attention as actual injuries. If a shelf nearly fell on someone but didn’t, the hazard is identical. The only difference is luck. Reassessing after near misses lets you close gaps before someone gets hurt.
When Workers Flag a Problem
Employees who report concerns, whether about physical hazards or work-related stress, should trigger an assessment. If someone tells their manager they’re experiencing stress linked to their job, an individual stress risk assessment is appropriate. This obligation extends to agency workers as well: before offering someone an assignment, the agency has a duty to find out what risks exist, and the host employer should include agency staff in their assessment process.
Worker feedback is one of the most reliable early-warning systems available. People doing the job daily will notice deteriorating conditions, awkward workarounds, or rising pressure long before a scheduled review catches them.
When Vulnerable Workers Are Involved
Certain groups face elevated risks that require specific, targeted assessments. Pregnancy is the most clearly defined trigger. Once an employer learns that a worker is pregnant, has given birth within the past six months, or is breastfeeding, they must check whether the existing workplace assessment covers any new risks to that person.
The hazards can be wide-ranging: lifting heavy loads, prolonged standing or sitting, exposure to infectious diseases or toxic chemicals, radiation, work-related stress, and long hours. These risks also shift as pregnancy progresses, so a single check at the announcement stage isn’t enough. The assessment should be revisited as conditions change throughout pregnancy and into the postnatal period.
Young workers and employees with disabilities similarly warrant individual assessments. A 16-year-old apprentice and a 40-year-old experienced operator face different levels of risk from the same piece of machinery, and the controls that protect one may not protect the other.
At Regular Scheduled Intervals
Even when nothing obvious has changed, risk assessments can become outdated. Equipment wears down, complacency creeps in, and subtle shifts accumulate. Regular reviews catch this drift. There is no single legally mandated frequency that applies to all workplace assessments, but common practice is to review them at least annually.
For health-related risk assessments, research suggests that rigid, one-size-fits-all intervals are inefficient. A 2024 study in BMJ Public Health examining cardiovascular risk screening found that five-yearly assessments were unnecessarily frequent for many low-risk individuals and not frequent enough for high-risk ones. The principle translates well to workplace settings: higher-risk activities and environments deserve more frequent review, while stable, low-risk operations can be reassessed on a longer cycle. The key is matching review frequency to actual risk level rather than checking a calendar box.
In Real Time: Dynamic Risk Assessment
Not every risk assessment happens at a desk with a form. Dynamic risk assessment is the practice of evaluating hazards on the spot, in real time, as conditions shift around you. It’s particularly relevant for workers in unpredictable settings: construction sites, emergency services, home visits, and outdoor work.
Several situations call for this kind of rapid, in-the-moment evaluation:
- Unpredictable weather: Rain turning a walkway into a slip hazard, wind making a lift unsafe, or sudden poor visibility all require immediate reassessment.
- Unfamiliar locations: Arriving at a new site and discovering uneven floors, hidden electrical risks, or blocked access routes that weren’t anticipated.
- Working alone: Without a colleague nearby to help in an emergency, a solo worker needs to continuously judge whether conditions remain safe enough to continue.
- Unexpected operational changes: A delivery arriving at the wrong time, a piece of equipment breaking mid-task, or an unauthorized person entering a work zone.
Dynamic assessments don’t replace formal written ones. They fill the gaps between planned reviews, covering the risks that no amount of advance planning can fully predict. Workers in high-variability roles should be trained to carry them out instinctively: pause, assess the new situation, decide whether to proceed, adapt, or stop.
How to Tell If Your Current Assessment Is Out of Date
If any of the following apply, your existing assessment needs updating: the workplace layout has changed, new people are doing the work, someone has been injured or reported a concern, new legislation or industry guidance has been published, or it’s been more than 12 months since the last review. A risk assessment that sits in a filing cabinet untouched isn’t protecting anyone. It only works as a living document that reflects what’s actually happening on the ground today.